1. Field of the Invention
The field of art to which the claims invention pertains is solid-bed adsorptive separation with an adsorbent comprising a zeolite. More specifically, the claimed invention relates to an improved process for the separation of a cresol from xylenol by employing a solid crystalline aluminosilicate adsorbent which selectively removes the cresol from the feed mixture. The cresol may then be recovered from the adsorbent through a desorption step which employs a desorbent material.
2. Description of the Prior Art
It is known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon species from mixtures thereof. In particular, the separation of normal paraffins from branched chain paraffins can be accomplished by using the type A zeolites which have pore openings from 3 to about 5 Angstroms. Such a separation process is disclosed for example in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the crystalline aluminosilicate adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
The type X or type Y zeolites have additionally been employed in processes to separate individual hydrocarbon isomers. In the processes described in U.S. Pat. Nos. 3,558,730; 3,558,732; 3,626,020; and 3,686,342, for example, they are used to separate desired xylene isomers; in U.S. Pat. No. 3,668,267 they are used to separate particular alkyl substituted naphthalenes.
More specifically, U.S. Pat. Nos. 3,014,078 and 3,969,422 teach the separation of cresol isomers by employing an adsorbent consisting of a crystalline zeolitic metalloaluminosilicate to selectively adsorb a cresol isomer from a feed mixture thereby producing a rich (cresol associated) adsorbent. In the preferred mode of operation, the adsorbed isomer is then removed by contacting with a displacement exchange fluid. Preferred displacement exchange fluids include phenol and alcohol, although other materials which may be employed include ethers, aromatic hydrocarbons, and paraffin hydrocarbons.
The present invention relates to a process for separating a cresol from a xylenol. In particular it has been found that a crystalline aluminosilicate is selective for cresol isomers as compared to xylenol isomers and may therefore be employed for separating cresols from xylenols.